As of mid-June, stocks of ProQuad were depleted because of manufacturing issues, and the combination vaccine was not expected to be available for the rest of the year, according to the Centers for Disease Control and Prevention. ProQuad is the combined attenuated live virus vaccine that contains measles, mumps, rubella, and varicella viruses—the components of the M-M-R II and varicella (Varivax) vaccines. Because of lower-than-expected yields of varicella-zoster virus (VZV), which is used to manufacture the Varivax, zoster (Zostavax), and ProQuad vaccines, their manufacturer, Merck & Co., had prioritized the production of Varivax and Zostavax over that of ProQuad. Then production of VZV bulk was temporarily suspended because of low yields.
The reduced supply of ProQuad was first announced in the CDC's Morbidity and Mortality Weekly Report (2007;56:453), which said that Merck had notified the CDC in February about the problem, and notified the CDC in May that projections of ProQuad orders indicated that the vaccine would no longer be available as of July, “although timing will depend on market demand.” Physicians can use M-M-R II and Varivax instead of ProQuad, according to the CDC notice.
It is expected that there will be an adequate supply of these vaccines to fully implement the recommended immunization schedule for varicella vaccine for all age groups and for the recommended use of zoster vaccine. For Varivax, this includes the routine two-dose schedule for children aged 12–15 months and 4–6 years; catch-up vaccination with the second dose for children and adolescents who received only one dose; and vaccination with two doses for other children, adolescents, and adults with no evidence of immunity.